The present invention relates to an electromagnetic clutch device for operating a clutch through which a drive power or a braking for are transferred.
An electromagnetic type friction clutch deice disclosed in Japanese Patent Application Laid-Open No. H11-287258 is comprised of an outer case composed of a front housing, made from non-magnetic material (aluminum alloy) and connected between a transfer and a transmission through a propeller shaft, and a rear housing made from magnetic material and screwed onto an opening of the front housing, an inner shaft connected to a rear def, an armature, an electromagnet, a cam mechanism, a first cam member, a second cam member spline connected to the inner shaft, a main clutch disposed between the front housing and the inner shaft, and a pilot clutch disposed between the front housing and the first cam member.
In such an electromagnetic type friction clutch device, a magnetic flux path (hereinafter referred to as a magnetic path) of the electromagnet is formed with a yoke of the electromagnet, the rear housing, the pilot clutch and the armature. Upon excitation of the electromagnet, a magnetic flux loop is formed in the magnetic path to allow the armature to be attracted. This causes the pilot clutch to be urged and coupled, with a transfer torque between the outer case and the inner shaft being applied to the cam mechanism. When this takes place, cam thrust force is created and applied through the second cam member to cause the main clutch to be coupled, and a drive power of an engine is transferred to rear wheels to allow a vehicle to fall in a four-wheel drive condition. Also, as the excitation of the electromagnet is interrupted, the pilot clutch is uncoupled to cause the thrust force of the cam mechanism to disappear and the main clutch is uncoupled to allow the vehicle to fall in a two-wheel drive condition.
Further, a vehicular def lock device disclosed in Japanese Patent Application Laid-Open No. S64-22633 is comprised of a bevel type differential mechanism, and a dog clutch disposed between a def case and a plunger, made from magnetic material, to lock resulting differential rotation, an electromagnetic type actuator for coupling the dog clutch, and a return spring for uncoupling the dog clutch.
The plunger is axially and moveably connected to a vehicle axle of a left side gear through a splined section and urged in a direction in which the dog clutch is uncoupled by a return spring.
The electromagnet type actuator is comprised of a plunger and an electromagnetic coil wound on a bearing housing, made from magnetic material, concentrically disposed on an outer periphery of the plunger, and the plunger and the bearing housing form a magnetic path of the electromagnetic coil. During a period in which the electromagnetic coil remains unexcited, the plunger responds to an urging force of the return spring and remains in a position to uncouple the dog clutch and unlock the differential lock of the differential mechanism. Also, as the electromagnetic coil is excited, a magnetic flux loop is created in the above-described magnetic path, and a resulting magnetic force results in a shifting operational force to shift the plunger rightward, rendering the dog clutch to be coupled thereby locking differential movement of the differential mechanism.